Nathaniel Bowditch (March 26, 1773 – March 16, 1838) was an early American mathematician remembered for his work on ocean navigation. He is often credited as the founder of modern maritime navigation; his book The New American Practical Navigator, first published in 1802, is still carried on board every commissioned U.S. Naval vessel.

Nathaniel Bowditch, the fourth of seven children, was born in Salem, Province of Massachusetts Bay, to Habakkuk Bowditch, a cooper who at one point was a sailor as well but stopped after his ship went aground in 1775, and Mary Ingersoll Bowditch. At the age of ten, he was made to leave school to work in his father's cooperage, before becoming indentured at twelve for nine years as a bookkeeping apprentice to a ship chandler. Here is where he first learned bookkeeping, an important step in his life.

In 1786, age fourteen, Bowditch began to study algebra and two years later he taught himself calculus. He also taught himself Latin in 1790 and French in 1792 so he was able to read mathematical works such as Isaac Newton's Philosophiae Naturalis Principia Mathematica. He found thousands of errors in John Hamilton Moore's The New Practical Navigator; at eighteen, he copied all the mathematical papers of the Philosophical Transactions of the Royal Society of London. Among his many significant scientific contributions would be a translation of Pierre-Simon de Laplace's Mécanique céleste, a lengthy work on mathematics and theoretical astronomy. This translation was critical to the development of astronomy in the United States.

Serendipity aided Bowditch's self-directed study, in as much as he found himself able to use the eminent Irish chemist Richard Kirwan's library: Hugh Hill, a privateer from Salem who captained the Pilgrim, had intercepted the ship carrying the library between Ireland and England and brought the library back to Salem in 1781.

In 1795, Bowditch went to sea on the first of four voyages as a ship's clerk and captain's writer. His fifth voyage was as master and part owner of a ship. Following this voyage, he returned to Salem in 1803 to resume his mathematical studies and enter the insurance business. One of his family homes in Salem, the Nathaniel Bowditch House, still exists and was restored in 2000. This house has been designated a National Historic Landmark.

In 1798 Bowditch married Elizabeth Boardman, who died seven months later. In 1800 Bowditch married his second wife and cousin, Mary "Polly" Ingersoll Bowditch (1781–1834). They had 2 daughters and 6 sons, including Henry Ingersoll Bowditch and William Ingersoll Bowditch. Among his grandchildren were Henry Pickering Bowditch and Charles Pickering Bowditch.

In 1802, his book The American Practical Navigator was first published. That same year, Harvard University awarded Bowditch an honorary degree.

In 1804, Bowditch became America's first insurance actuary as president of the Essex Fire and Marine Insurance Company in Salem. Under his direction, the company prospered despite difficult political conditions and the War of 1812.